This invention relates to an article of extruded plastic wherein one end thereof has a varying physical characteristic from the other end thereof, e.g., varying flexibility, including the method and apparatus for producing such an article.
An example of an area where such an article might be used is the medical field such as a substitute for presently available catheter tubes. It is desirable in such catheter tubes that one end be relatively stiff while the other end by relatively flexible such that the more flexible lead end aids in insertion and is less traumatic once inserted into the body vessel by the doctor or medical technician. For this purpose, it is now known to join two hollow extruded plastic tubes of dissimilar flexibilities by a melt bonding technique, i.e., the butt ends of the tubes are heated to the softening point, and the adjacent areas fused to join their ends to form a continuous tube of dissimilar flexible ends. It is also known to adhesively connect the base ends of such tubes as by radio frequency bonding to form the desired result. However, such connections can and sometimes do fail under use such as upon being pressurized for injection (e.g., injection of contrast media); and, accordingly, a less labor intensive and more fail-safe article including such above-mentioned physical characteristics is needed.
Accordingly, the primary object of this invention is to supply such an article that is highly reliable yet can be produced at a reasonable cost.
Another and further object of the present invention is the provision of a method and apparatus for reasonably and assuredly forming such articles as indicated above.
These and other objects of the present invention are accomplished by the provision of a continually melt extruded length of article comprising first and second terminal end portions formed of compatible first and second melt mixable plastics and an intermediate connecting portion connecting joining said end portions wherein said first and second end portions have varying physical characteristics such as flexibility and said intermediate portion being a melt extrusion blending of said first and second plastics. The above article is formed in an unique melt extrusion process wherein two extruders are connected at a common head, and a gear assembly receives the output of such extruders such that the gear system may be driven between first and second positions in which similar, i.e., compatible, plastic resins from the extruders are alternately directed into an extrusion die such that a bridging section of mixed resins is formed as a connecting portion. The dwell period in which the dissimilar resins are mixed is of very short duration such that a fairly pronounced demarcation line is formed between the two end portions of the article length.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.